(349a) Continuous Flow Synthesis of Mfu-4l/Mfu-4l-OH and Their Application in Carbonate Dehydration

Metal-Organic Frameworks (MOFs) are promising functional materials with high porosity and excellent structural tunability. Utilizing these unique characteristics, MOFs have demonstrated their potential in a wide range of applications as adsorbents and catalysts. In particular, MFU-4l, Zn₅Cl₄(BTDD)₃, is considered an ideal water sorbent, offering a high water uptake capacity (~1 g_water/g_MOF) and a sharp water uptake step at a relative humidity of 65%, making it easily deployable across humid environments. Furthermore, with post-synthetic exchange of MFU-4l, MFU-4l-OH can be utilized as a structural mimic of carbonic anhydrase for CO₂ hydration and CO₃^2- dehydration reactions.

Regardless of the high-water uptake and unique structural characteristics, implementation of MFU-4l and MFU-4l-OH remains challenging due to long reaction times and large solvent volume requirements. One critical limitation of the organic linker, H₂BTDD, is its poor solubility in solvents (1 g_BTDD/1 L_DMF), requiring a massive amount of N, N-dimethylformamide (DMF) in a scale-up synthesis. This inherent challenge couples with the heat and mass transport limitations of a batch reactor, resulting in low productivity and poor nucleation/growth control as well as contributing to high production cost and safety concern in handling and heating large amounts of hazardous solvents.

To overcome the limitations, we utilize a flow reactor, which allows process intensification, rapid optimization of synthesis parameters by screening wider parameter space in shorter time frames, and relative ease of scale-up compared to the batch reactors. Here, we investigate the use of a flow reactor for accelerated synthesis of MFU-4l under solvothermal conditions and scaling up the synthesis via parallelization of flow reactors without sacrificing the product yield and crystallinity. We map the chemical design space with an overall goal of minimizing the use of the solvent (DMF) for synthesis and demonstrate the feasibility of recycling DMF (~80% by volume) for consecutive MFU-4l synthesis. We model the kg-scale synthesis using ASPEN process modeling software to evaluate the mass and energy balances for the synthesis that incorporates a solvent recycle loop.

Finally, we post-synthetically exchange chlorine on MFU-4l with hydroxide, structurally mimicking the metalloenzyme, carbonic anhydrase. MFU-4l-OH shows an enhanced carbonate dehydration rate, demonstrated with a packed bed reactor using a CO₂ permeable membrane. With the developed system, we showed continuous degassing of the carbon dioxide out of the aqueous solution targeting the carbonate clearance module for low-temperature oxygen evolution reaction (OER). Overall, this work demonstrates new pathways for scaling-up MFU-4l synthesis using parallelized flow reactors towards sustainable manufacturing and for a promising application of MFU-4l-OH.